Ergonomics may be defined as an engineering and physiological study of relationships between man and machines. An ergonomic device may be a device that is tailored to reflect human structure and function to, for example, enhance a person's ability to operate the device or an adjacent apparatus.
An ergonomic device may enhance a worker's performance or ability to operate a machine by relieving fatigue. For example, fatigue or repetitive motion disorders of the hand, wrist, and arm may be caused by repetitive or tedious hand, wrist, and arm functions. In the computerized environment, keyboard operators may spend their entire workdays at terminals with their forearms extended to their keyboards. Postal workers may spend long periods of time with their forearms extended to operate coding machines for coding and sorting mail. Assembly-line personnel may also work with their forearms extended over articles of manufacture to manipulate tiny parts with their fingers.
Ergonomic arm support devices have been designed for supporting the forearm of keyboard operators. Each of these devices typically consist of two arms with one arm secured to a desk and the second arm having a cushion at its distal end for supporting the forearm. These arms are frequently jointed at their connection, and also may be jointed at the forearm cushion and at the connection to the keyboard table for a total of three joints.
These jointed arm support devices have a number of problems. For example, the inclusion of two arms and three joints for a single device requires that the arm be secured to the keyboard table and positioned at a relatively great distance from the keyboard in order to provide sufficient space for mounting the jointed arm. Accordingly, a pair of such arm support devices may require a larger desk, and therefore may disadvantageously occupy a greater amount of work space than is otherwise required. If the arm supports are in fact mounted closer to the terminal, the range of motion of each of the arm supports is limited, and the arm supports may dig into a worker's torso or interfere with his or her chair.
A similar problem concerns the impracticality of mounting the conventional jointed arm support on a chair. If this type of arm support is mounted on a chair, the long reach of its jointed two arms may interfere with access to the seat of the chair. Furthermore, the jointed arm support simply may not be reasonably operable on a chair because a chair, by its very nature, is drawn adjacent to the keyboard to a position in which the torso of the occupant of the chair or the keyboard may interfere with a range of motion of the second arm.
Another problem with the conventional jointed arm support is that it easily breaks when leaned upon. It is typical behavior for a worker to lean and exert downward pressure or weight on the cushioned or distal end of the second arm of the conventional arm support which is intended for supporting only the weight of a forearm. The leverage or force exerted by the weight of such a lean or end loading is magnified by the overall length of the two arms of the jointed arm support.
Still another problem with the jointed arm support is that it is difficult to maneuver. For example, when one arm is aligned directly over the other arm, and the intended direction of movement of the forearm is in line with the two arms, the arms initially resist pivoting relative to each other until the forearm exerts a force out of alignment with the two arms. Accordingly, such a conventional jointed arm support may not meet the definition of an ergonomic device that typically tracks or follows a natural movement of the human body without resistance.
Yet another problem is that the conventional two-arm jointed arm support may not decrease substantially the risk of carpal syndrome. This syndrome may be caused at least in part by the tendency of a keyboard operator to rest his or her wrists on the keyboard, or on a portion of the table immediately in front of the keyboard, while his or her hands are elevated relative to the wrists for operation of the keyboard. With the long reach of the two-arm jointed arm support, and the attendant amount of leverage, the arm cushion on the distal end of the second arm may sink to the table surface even under the relatively light weight of an arm. Even providing for height adjustment, such instability or deflection of the second arm may not provide a sufficient lift for the wrists to be held at the proper elevation relative to the hands to minimize the risk of carpal syndrome.